ARCHIVED REPORTS_XR0009603 - Laserfiche WebLink

Home Browse Search

Case Closure Report Former Tosco (Unocal) SS No 5421, Stockton, California July 8, 1998 • On October 26, 1992, the former leach field/seepage pit (located at the southwest corner of the referenced site) was excavated over an area of approximately 29 feet by 30 feet to a depth of about 25 feet bgs Three soil samples, labeled SW-2, SW-3 , and SW-4, were collected from the sidewalls of the new excavation at depths ranging from 23 feet to 24 feet bgs In addition, one soil sample, labeled B(25), was collected from the bottom of the new excavation at a depth of approximately 25 feet bgs Mr Knoll was also present during excavation and sampling activities These samples were also collected from bulk material excavated by backhoe Sample point Iocations and analytical results are presented in Appendix A Tables 1C and 2C, Figure 1C All excavated soil was stockpiled on-site prior to disposal of at Laidlaw Environmental Services (an approved Class II disposal site) Samples were analyzed for TPH as gasoline by EPA Method 503018015, BTEX by EPA Method 8020, TPH as diesel by EPA Method 3550/8015, total oil and grease (TOG) by Standard Methods 5520 E&F, volatile organic compounds by EPA Method 8240, and for TCLP metals (arsenic, barium, cadmium, chromium, lead, mercury, selenium, and silver) The analytical results for the soil samples P-1 through P-6 (collected from the leach lines) and S(9) (collected from beneath the former septic tank) indicate non-detectable concentrations of TPH as gasoline, BTEX, TPH as diesel, EPA 8240 constituents, and TOG The analytical results of the soil samples B(25) and SW-1 through SW-4, collected from the former leach field/seepage pit excavation, indicated non-detectable concentrations of TPH as gasoline, benzene, and EPA 8240 constituents TPH as diesel concentrations ranged from non-detectable to 13 ppm and TOG concentrations ranged from non-detectable to 84 ppm, except for sample B(25), which contained 210 ppm of TOG The results of the TCLP metal analyses are presented in Appendix A Table 2C Unocal received a Underground Injection Control (UIC) closure letter on March 9, 1994 from the US EPA regarding the removal of the septic tank, leach field and seepage pits A copy of the US EPA UIC Closure letter is presented in Appendix B Abandoned Water Well Destruction Activities A well destruction work plan dated July 19, 1990 was prepared by KEI for the destruction of the abandoned water well located on-site Destruction of the abandoned water well was completed on January 24, 1992 During the initial phase of the septic tank removal activities (July 15, 1992), a second water well consisting of a seven-inch steel casing, was encountered about 40 feet southwest of the monitoring well MW-1 On August 4, 1992, a representative of KEI was on-site during a downhole video camera survey of this well The survey was conducted by Water Well Technology, Inc of Rancho Cordova, California The downhole camera survey indicated that the depth of the well is 78 feet below trade and that the casing extends to 72 feet below grade Possible perforations in the casing were 140162 03 6